record.py

import spidev
import time
import numpy as np
import sys

import adxl355

################################################################################
# Some values for the recording                                                #
################################################################################
# Filename for output
outfilename = 'output.csv'
# Measurement time in seconds
mtime = 1
# Data rate, only some values are possible. All others will crash
# possible: 4000, 2000, 1000, 500, 250, 125, 62.5, 31.25, 15.625, 7.813, 3.906 
rate = 62.5

################################################################################
# Initialize the SPI interface                                                 #
################################################################################
spi = spidev.SpiDev()
bus = 0
device = 1
spi.open(bus, device)
spi.max_speed_hz = 5000000
spi.mode = 0b00 #ADXL 355 has mode SPOL=0 SPHA=0, its bit code is 0b00

################################################################################
# Initialize the ADXL355                                                       #
################################################################################
acc = adxl355.ADXL355(spi.xfer2)
acc.start()
acc.setrange(adxl355.SET_RANGE_2G) # set range to 2g
acc.setfilter(lpf = adxl355.ODR_TO_BIT[rate]) # set data rate


################################################################################
# Record data                                                                  #
################################################################################
datalist = []
t0 = time.time()
tc = time.time()

msamples = mtime * rate
mperiod = 1.0 / rate

datalist = []
acc.emptyfifo()
while (len(datalist) < msamples):
    if acc.fifooverrange():
        print("The FIFO overrange bit was set. That means some data was lost.")
        print("Consider slower sampling. Or faster host computer.")
    if acc.hasnewdata():
        datalist += acc.get3Vfifo()

# The get3Vfifo only returns raw data. That means three bytes per coordinate,
# three coordinates per data point. Data needs to be converted first to <int>,
# including, a twocomplement conversion to allow for negative values.
# Afterwards, values are converted to <float> g values.

# Convert the bytes to <int> (including twocomplement conversion)
rawdatalist = acc.convertlisttoRaw(datalist)
# Convert the <int> to <float> in g
gdatalist = acc.convertRawtog(acc.convertlisttoRaw(datalist))

# Add a column with a timestamp
alldata = []
for i in range(len(gdatalist)):
    alldata.append([0, i * mperiod] + gdatalist[i])

# Save it as a csv file    
alldatanp = np.array(alldata)
np.savetxt(outfilename, alldatanp, delimiter=",")